Department of Aerospace Information Engineering, Konkuk University, Seoul 05029, Korea.
Artificial Muscle Research Center, Konkuk University, Seoul 05029, Korea.
Sensors (Basel). 2020 Dec 15;20(24):7185. doi: 10.3390/s20247185.
A thermal protection system (TPS) is designed and fabricated to protect a hypersonic vehicle from extreme conditions. Good condition of the TPS panels is necessary for the next flight mission. A loose bolted joint is a crucial defect in a metallic TPS panel. This study introduces an experimental method to investigate the dynamic characteristics and state of health of a metallic TPS panel through an operational modal analysis (OMA). Experimental investigations were implemented under free-free supports to account for a healthy state, the insulation effect, and fastener failures. The dynamic deformations resulted from an impulse force were measured using a non-contact three-dimensional point tracking (3DPT) method. Using changes in natural frequencies, the damping ratio, and operational deflection shapes (ODSs) due to the TPS failure, we were able to detect loose bolted joints. Moreover, we also developed an in-house program based on a modal assurance criterion (MAC) to detect the state of damage of test structures. In a damage state, such as a loose bolted joint, the stiffness of the TPS panel was reduced, which resulted in changes in the natural frequency and the damping ratio. The calculated MAC values were less than one, which pointed out possible damage in the test TPS panels. Our results also demonstrated that a combination of the 3DPT-based OMA method and the MAC achieved good robustness and sufficient accuracy in damage identification for complex aerospace structures such as TPS structures.
热防护系统（TPS）旨在保护高超音速飞行器免受极端条件的影响。TPS 面板的良好状况对于下一次飞行任务是必要的。在金属 TPS 面板中，松动的螺栓连接是一个关键缺陷。本研究通过运行模态分析（OMA）介绍了一种通过实验方法来研究金属 TPS 面板的动态特性和健康状态的方法。实验研究在自由支撑下进行，以考虑健康状态、隔热效果和紧固件失效。使用非接触式三维点跟踪（3DPT）方法测量了脉冲力产生的动态变形。通过自然频率的变化、阻尼比和由于 TPS 失效导致的工作挠曲形状（ODS），我们能够检测到松动的螺栓连接。此外，我们还基于模态保证准则（MAC）开发了一个内部程序，用于检测测试结构的损伤状态。在损伤状态下，例如松动的螺栓连接，TPS 面板的刚度降低，导致自然频率和阻尼比发生变化。计算出的 MAC 值小于 1，这表明测试 TPS 面板可能存在损伤。我们的结果还表明，基于 3DPT 的 OMA 方法和 MAC 的组合在复杂航空航天结构（如 TPS 结构）的损伤识别中具有良好的鲁棒性和足够的准确性。
